PHOTOREGULATION OF PERMEABILITY ACROSS A MEMBRANE FROM A GRAFT COPOLYMER CONTAINING A PHOTORESPONSIVE POLYPEPTIDE BRANCH

The first example of the photoregulation of the permeability across a membrane containing a polypeptide by photoinduced conformational change of the polypeptide chains without any concomitant change in electrostatic repulsion along the polypeptide chain was achieved. A new polyvinyl/polypeptide graft copolymer composed of a photoresponsive copolypeptide branch from β-p-phenylazobenzyl L-aspartate and β-benzyl L-aspartate attached to a poly(butyl methacrylate) backbone was synthesized and the membrane was prepared. The permeation rate of mandelic acid across the membrane immersed in trimethyl phosphate (TMP) was raised by about six times with UV irradiation and was suppressed on irradiation with visible light. The permeation rates of other polar and nonpolar substrates such as N-((benzyloxy)carbonyl)-D, L-alanine, acetone, and biphenyl were also raised with UV irradiation and were suppressed on irradiation with visible light. The photoinduced permeability change thus observed is correlated to the conformational change of the polypeptide chains in the membrane. In the CD spectrum of the membrane immersed in TMP, the UV irradiation changed the sign of the CD band associated with the peptide n-π* transition from positive at 215 nm to negative at 222 nm within 15 min, and the original CD profile was recovered by irradiation with visible light within 5 min or by standing in the dark for about 5 days, indicating the inversion of the helix sense of the polypeptide chains in the membrane from left-handed to right- handed with UV irradiation and the reversion on irradiation with visible light or dark adaption. © 1990, American Chemical Society. All rights reserved.